In the field of locks for sliding glass doors, many of the commonly used locks have not been certain in their locking operation and have been relatively easily broken or tampered with. Most such locks have not had the capability for securely maintaining a door in a partially opened condition. Standard latches usually involve hooking onto the soft aluminum door frame. Such hooks can be easily forced.
Typical of attempts to overcome such deficiencies is U.S. Reissue Pat. No. 27,161 issued to Raymon as U.S. Pat. No. 3,420,001 on Jan. 7, 1969 and reissued on Aug. 10, 1971. That patent refers to a locking bar of adjustable length pivotally mounted at one end. In its operative locking position the bar is disposed in the horizontal guide track for the panel, and extends therein in a plane parallel to the plane of sliding movement of the panel. In the inoperative position the bar is disposed in the vertical channel guide track for the panel. The adjustable locking bar in its operative position has its free end engaged against the rear edge of the panel to prevent the panel from being moved rearwardly. Clamping means are positioned in the vertical channel guide track for releasably maintaining said locking bar in the inoperative position.
When confronted with a latching bar referred to in Raymon, an intruder need only slip a coat hanger between the frames of the glass door and pull up on the latching bar in order to free the door for opening. Furthermore, to disengage Raymon, the occupant must bend over and lift the latch from its operative position at floor level to its inoperative vertical position.
Another approach is referred to in Hakanson, U.S. Pat. No. 3,352,586, issued Nov. 14, 1967. Hankanson refers to a locking device for sliding windows and doors in which the end of a pivotable lock member mounted on a movable frame engages any one of the teeth of a corrugated member mounted on a stationary frame. A control member controls the positioning of the lock member and blocks it against disengagement from the corrugated member. In order to release the locking device, it is necessary to pull downwardly on pull chain 29, causing the control member 22 to pivot in a clockwise direction against the urging of spring 32.
Hankanson relies upon the integrity of a pawl and ratchet teeth and upon the security with which the corrugated member 35 is affixed to the top of a door frame. Such door frames are usually made of a soft aluminum.